CO2 and Smoke detectors have an internal sensor that has a design life of 5 years from the date of manufacture. After the 5 years you start getting false alarms due to the sensor itself exceeding its average life span. On the combination CO2 and Smoke deterctors you will often see a manufacture date or a replace by date inside the cover on the main board.
On AC powered models such as this one you will just get the error when the sensor fails. If you got the full 5+ years out of your CO2 sensor then you should be happy that it served a full life expectancy.
Some Wiki data on CO2 detectors:
http://en.wikipedia.org/wiki/Carbon_monoxide_detector
This paragragh appears under installation
The gas sensors in CO alarms have a limited and indeterminable life span, typically two to five years. The test button on a CO alarm only tests the battery and circuitry not the sensor. CO alarms should be tested with an external source of calibrated test gas, as recommended by the latest version of NFPA 720.
Alarms over five years old should be replaced but they should be checked on installation and at least annually during the manufacturers warranty period.
Thanks for choosing FixYa.
Kelly
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